Author Topic: Celestron VX Mount  (Read 8887 times)

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Offline Chris Duffey

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Celestron VX Mount
« on: March 15, 2015, 11:35:41 AM »
Greetings all,  I just got Satellite Tracker 2.5.1 working with my mount and discovered something I think is odd,  I don't know if it is mount specific but thought I'd throw the question here.  Last night I was out making images etc.. the telescope was perfectly polar aligned and at the end of my imaging session I thought I'd test the tracker software.  Well the telescope kept trying to point through the earth, I checked the time and position and all seemed to be right.  This morning I was looking at it and decided to try changing the sign of the longitude to + instead of negative and now it seems to be pointing in the right direction, but this makes no sense since I live in California !!!! the Longitude should be negative.  But that brings up another thing - the location input has hardcoded N and E for the latitude and longitude... So basically I am confused by the whole thing, It seems to be working well now but I hate not understanding the "why".

Offline John Eccles

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Re: Celestron VX Mount
« Reply #1 on: March 20, 2015, 10:40:35 PM »
Chris,

Okay I did a little experiment. Take a look at this website: http://www.calculatorcat.com/latitude_longitude.phtml  Type in the name of your city and take a look at the Decimal Degrees on the middle left of the page. You will notice that the Latitude is positive and the Longitude is negative. This is representative of a location relative to North and West. In order to represent it as North and East one would have to switch the sign of the Longitude to positive. To verify that go to this website: http://www.calculatorcat.com/latitude_longitude.phtml  Type in the Latitude and Longitude as per your location relative to North and West as per the previous website's information (the first website indicated in this message) using the negative Longitude representing west. Then click on "Decimal to Minutes-Seconds >=". Now change the Longitude drop down from W to E and then click on "=<Minutes-Seconds to Decimal". You will see the sign change to positive on the decimal value of the Longitude and this represents the value relative to East. I hope this clarifies what you are seeing.

As a check take a look at this website: http://www.gpscoordinates.eu/show-gps-coordinates.php  Navigate on the map to your location. Notice that the GPS coordinates are stated as North and West with the Longitude being a negative number for the decimal value. To represent the Longitude as East make the Longitude positive for your location.

John

Update: Something is amiss here. Apparently the labeling on the Satellite Tracker application is a bit misleading as can be seen by the further explanation below by Chris. The labeling must not be hard coded but made variable based on the actual position of the viewer.
« Last Edit: March 21, 2015, 08:43:38 PM by John Eccles »
Regards, John Eccles, Owner of Satellite Tracker Application, the Satellite Tracker Forum, and the Yahoo Groups called Satellite Tracker

Offline Chris Duffey

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Re: Celestron VX Mount
« Reply #2 on: March 21, 2015, 05:37:05 PM »
John, you almost had me ! but I'm not sure this is a validation of the correctness of having a + longitude in California, since it looks like the gui just changes the sign based on whether E or W is selected, thereby making sure that the user doesn't make a mistake.  Its pretty much defined that a longitude west of the prime meridian must be negative and east of the prime meridian is positive, the only discontinuity is at longitudes of 180 degrees.  Designating the direction with compass ordinals is just a convenient way to ditch the sign, in essence West = a negative sign and east = a positive sign.  It is usually customary for geo software to either have a selector for East/West and North/South OR require the user to enter the sign and do not reference the ordinals at all.  the location of my house with a positive longitude (East of the prime meridian) ends up in China somewhere. What the Satellite Tracker GUI shows is incorrect, My longitude is never going to be East of the Prime Meridian, and if we are dealing with the mathematical version of my longitude it must be negative.  I'm guessing that since making the value positive "fixes it" there is a sign inversion somewhere in the source

Offline John Eccles

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Re: Celestron VX Mount
« Reply #3 on: March 21, 2015, 05:50:10 PM »
Chris,

I'm wondering why no one else has caught this problem. This software has been in existence for many years. There must be something else going on here. Maybe someone else who reads this can chime in. Which version of the software are you using? I would suggest you use version 2.4.9b which is the last version published by the previous owner. In the process of going to the latest version 2.5.1 I may have messed up something.

John
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Offline Chris Duffey

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Re: Celestron VX Mount
« Reply #4 on: March 21, 2015, 06:20:48 PM »
John,

I agree it is kind of a fundamental thing, I am running 2.5.1 but will go try the older version,  - I may take a look at the code myself, it could be that there is some coordinate rotation that occurs.  I have experience with writing software to point RF antennas and cameras on aircraft (a problem complicated by the fact you have a platform that is constantly changing its body angles), the math is not complicated but there are numerous opportunities to invert a sign by accident.  It would be interesting to see if internally the software uses a NED convention (North, East, and Down are positive) or NEU or some other typical convention, this could give us a clue as to what is going on

I appreciate you looking at this !

Chris

Offline Chris Duffey

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Re: Celestron VX Mount
« Reply #5 on: March 21, 2015, 07:14:38 PM »
I found the problem !! Not that cosmic, So I noticed in the manual that the UTC offset was negative, I had assumed the software would automatically make that value negative, but apparently this must be entered - so now that I have -7 hours instead of +7, putting in a negative sign for the longitude makes it work - so really there is only one little issue, and it is purely cosmetic, the coolest thing to do would be to get rid of the N and E on the Satellite Tracker GUI entirely since it is not correct unless you happen to be North of the equator and east of Greenwich England :-) We could add something to decode the sign entered by the user and display N/S and E/W

Offline Chris Duffey

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Re: Celestron VX Mount
« Reply #6 on: March 21, 2015, 07:44:35 PM »
Excited to go track stuff tonight !! FYI I used my iPhone level app to measure the elevation of the tube and verify against the computed elevation in the Object Data window, they match perfectly (90 - iPhone level value = Satellite Tracker elevation) !! so it looks good to go !

Offline John Eccles

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Re: Celestron VX Mount
« Reply #7 on: March 21, 2015, 08:12:35 PM »
Chris,

Glad you got to the bottom of the problem. I guess I could add to the todo list this change that you are requesting. I will do this sometime in the next couple of days, time permitting.

In sum, what you are saying is that by having the fixed GUI of N (North) and E (East) that this labeling is incorrect for the locations that we are using here in the US? Going back to the example in my previous post I had a feeling that something wasn't quite right since I enter my position here as Latitude of 34.6695367 and Longitude of -79.9827636. Well, according to my example that is North and West. That kind of puzzled me but I was thinking of your problem and solution. In actuality the labeling for my location should reflect North (N) and West (W). Are you in agreement with that? If so, then I can modify the software to update the labeling accordingly. That shouldn't be too hard to do. Now if the value just happens to be zero for Longitude what do we display - E (East) or W (West)? Same goes for Latitude.

John
« Last Edit: March 21, 2015, 08:40:24 PM by John Eccles »
Regards, John Eccles, Owner of Satellite Tracker Application, the Satellite Tracker Forum, and the Yahoo Groups called Satellite Tracker

Offline Chris Duffey

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Re: Celestron VX Mount
« Reply #8 on: March 22, 2015, 08:29:39 AM »
Hi John,

You are correct, by labeling N and E in the US/Canada,  it is technically incorrect (anywhere west of the Prime Meridian), I am in agreement with your example.  For the case of zero latitude or zero longitude, since ST uses decimal degrees you just have a really small number that are either just to the east or west of the Prime Meridian or just north or south of the equator, if you decoded the N/S E/W ordinals based on the sign entered by the user and then displayed N/S and E/W next to the Lat/Lon input boxes then it will be in agreement with the users presumed entry.  For the discontinuity that exists where the longitude goes from -180 to +180 the same rules apply, if the user enters a negative sign he is stating that he is at a west longitude.  The other way to do this of course is to let the user pick the ordinal and determine the sign from that, I'm not a huge fan of this approach but it would be accurate as well and some people might prefer it

Offline Ulf Granlund

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Re: Celestron VX Mount
« Reply #9 on: July 10, 2015, 01:26:49 PM »
Hi, I am experimenting with Satellite Tracker (v 2.6.1) and  a Celestron VX mount, and from this thread it appears that this should work. Can somebody please explain which of the available telescope interface protocols I should select to make it work. I tried the Celestron 5/8 protocol, but that seemed to produce strange results, and afterwards the hand control was printing strange carachters on the display and I had to reset it.
Regards Ulf

Offline Ulf Granlund

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Re: Celestron VX Mount
« Reply #10 on: July 12, 2015, 03:22:50 PM »
I have tried to investigate the compatibility and history of different versions of Celestron hand controls, in order to see which of the available options in Satellite Tracker that would be closest to my Celestron VX mount, which has the Nexstar+ hand control. Based on this link:

http://www.nexstarsite.com/PCControl.htm

it would appear that the Celestron CGE is the most modern of the available options in Satellite Tracker, and there appears to be reasons to believe that the communication protocols for the CGE and the Nexstar+ are in fact the same. However, I have contacted Celestron support to get this verified. I will post again when I get a reply.
Regards
Ulf

Offline Ulf Granlund

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Re: Celestron VX Mount
« Reply #11 on: July 17, 2015, 07:11:07 PM »
The reply from Celestron support is that the present day Nexstar+ hand controls that is used by the VX mount and most other Celestron scopes/mounts of today uses the same serial communication protocol as previous v4 hand controls that was used by for example the CGE models. Hence the CGE option in Satellite tracker should work with the VX mount. The communication protocol is described in the enclosed document, which support says is the only available documentation there is on this protocol, and hence the document is valid also for the VX mount and all other mounts using the Nexstar+ hand control.

Offline John Eccles

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Re: Celestron VX Mount
« Reply #12 on: July 18, 2015, 06:51:54 PM »
Thank you for posting the Celestron reply. I do have that documentation and it was provided as a .zip file some time ago by another user which was dated July 29, 2006 and it appears to be the same document that Celestron provided.
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